The time-of-flight mass spectrometry (TOFMS) is very often used for analysing gas [1].
This technique makes it possible to detect the species present in a gas according to their time of travel in a so-called free-flight zone.
To this effect, the gas to be analysed is ionized, which then makes it possible to separate the various species according to their mass to charge ratio, which is usually noted as m/z, where m is the mass of the ion (generally expressed in Daltons (Da)) and z the number of elementary charges.
The ionized species are injected with a certain speed into an electrostatic field.
The forces that are exerted on the ions then modify their trajectory according to the mass to charge ratio of the latter.
The time-of-flight mass spectrometer is based on the measurement of a time of travel that is specific to each species in a so-called free-flight zone, which is a zone devoid of any electrostatic field, wherein the ions move away from one another according to their mass to charge ratio.
The lightest species therefore arrive on a detector placed at the outlet of this free-flight zone before the heaviest species; the mass to charge ratio of each species can then be deduced from the value of the time of flight.
In conventional mass spectrometers, the free-flight zone has a length of about a metre, which imposes a very substantial size, allowing the mass spectrometer to be used only in the laboratory.
For the last ten years or so, various teams have proposed miniaturising these analysis systems in order to make them portable [2] [3].
However, these systems remain either voluminous (as such, “mini” spectrometers have a mass of several kg), or are very little resolved in mass, recalling that the mass resolution of a mass spectrometer refers to the ratio m/Δm, where Δm is the smallest difference in mass that can be measured between two neighbouring peaks, which characterises the ability of the spectrometer to distinguish two peaks corresponding to two species that have a difference in mass Δm.
As such, on miniaturised mass spectrometers, a resolution typically between 10 and 50 on masses between 1 Da and 200 Da is observed, while on commercial time-of-flight mass spectrometers with the highest performance (but which have a size of a few m3), the resolution is from several thousand to 20,000 on ranks of mass from 1 Da to 10,000 Da [2] [4].
A purpose of the invention is therefore to design a gas analysis system that incorporates a time-of-flight mass spectrometer and at least one gas phase chromatography column, having the form of a small-size portable integrated system (with the target mass being less than 1 kg) while still having a reasonable resolution over a wider measurement range than that of the existing miniaturised mass spectrometers.
For the purposes of information, the resolution sought is about from 1000 to 2000 on a rank of mass from 0 to 2000 Da.